It is known to use face sealing annular valves to regulate the flow of hydraulic fluid into or out of a piston cylinder, or other working chamber of a fluid-working machine. In annular valves of this type, a ring-shaped fluid path is selectively sealed by a similarly ring-shaped annular valve member. Annular valves are advantageous as they can provide a relatively large cross-sectional area through which hydraulic fluid can flow into or out of a working chamber.
It is desirable for face sealing annular valves to be relatively small, in order to reduce the diameter of, the annular valve and therefore the size of fluid-working machine. It is also desirable for annular valves to be formed from as few parts as possible, and with as large tolerances as possible, while still fulfilling appropriate application-specific performance criteria, such as operating lifetime.
A problem which arises with known annular valve members is the difficulty of forming good inner and outer sealing lines in order to create an effective seal. The tolerance required for the valve seats and annular valve member are very small. If one of the inner sealing line or outer sealing line is formed before the other, then in known valves, the other sealing line will not be complete and sealing will be poor. Therefore, the invention addresses the technical problem of providing annular valves which reliably form seals.
Generally, in known valves in which inner and outer sealing lines form at the same time, the inner and outer sealing lines, between the annular valve member and the valve seat must be in a plane perpendicular to the axis of movement of the annular valve member to avoid one sealing line forming before the other. However, it can be desirable to have inner and outer sealing lines which are not in a plane perpendicular to the axis of movement of the annular valve member, for example, to reduce the size of the valve or to simplify the provision of flow passages through the valve. Thus, some embodiments of the invention particularly address the problem of forming an effective seal in embodiments where the inner and outer sealing lines are not in a plane perpendicular to the axis of movement of the annular valve member.